Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine and a printer that uses an electrophotographic system or an electrostatic recording system.
Description of the Related Art
Among image forming apparatuses, digital laser beam printers of a so-called electrophotographic system have been known. In a development device equipped in the image forming apparatus, a one-component developer containing magnetic toner as a main component, or a two-component developer containing non-magnetic toner and magnetic carrier as main components has been used. In particular, in the image forming apparatus that forms a full-color or multi-color image, the two-component developer has been mainly used from the viewpoint of color of an image or the like.
There is a toner supply control as particular importance in the two-component developer. The two-component developer has the toner and the carrier, and when forming the image, a TD ratio as a ratio of the toner to the carrier changes by consumption of the toner. Since charging characteristics of the toner change depending on the value of the TD ratio, it is required to supply the toner so as to maintain the charging characteristics of the toner. A toner bottle configured to supply the toner is provided separately from the development device, and when there is no toner in the toner bottle, the toner bottle is replaced with a new one.
As a unit of determining that there is no toner (toner absence) in the toner bottle, there is a method as in US Patent Application Publication No. 2005/063714 A1. Specifically, a toner density sensor configured to detect the TD ratio of the two-component developer is equipped in the development device, and toner absence is determined according to the value thereof. Furthermore, there is a method (toner remaining amount checking sequence) of checking whether the TD ratio of the two-component developer rises from the value of the toner density sensor after the supply of toner, and determining the toner absence from the result so as to increase the accuracy of toner absence.
However, in the case of a configuration in which the toner remaining amount checking sequence is performed, the following problems may occur.
When the remaining amount of toner in the toner bottle decreases (just before toner absence), toner capable of being supplied to the development device decreases. For this reason, even in the image with less toner consumption, the TD ratio of the two-component developer decreases, and the toner remaining amount checking sequence starts.
However, even if the toner remaining amount checking sequence is performed, since the amount of toner supplied into the development device is small, the TD ratio of the two-component developer does not increase. For this reason, in some cases, the toner remaining amount checking sequence may be unnecessarily repeated. In this case, there has been a problem in that downtime due to the toner remaining amount checking sequence frequently occurs until “toner absence” is displayed. That is, in regard to the toner remaining amount checking sequence, there has been a problem of compatibility between the control time and the detection accuracy of “toner presence” and “toner absence”.
Here, when simply limiting the toner remaining amount checking sequence so as to simply shorten the downtime, there is a risk of a drop of the detection accuracy of the toner density.